Cleaner Air Delaware

Air Quality Monitoring

Delaware recognizes public health, the environment, and the economy as key components in finding solutions to air pollution. DNREC has worked to develop effective and publicly-acceptable plans to reduce emissions while limiting the financial impact on the regulated community. Innovative permitting and compliance procedures, which allow for environmental protection as well as flexibility for commercial and industrial operations to adhere to regulatory requirements, provide the state the ability to support the economy while lessening health risks.
The federal Clean Air Act of 1970 established the National Ambient Air Quality Standards (NAAQS) for criteria pollutants considered harmful to public health and the environment. DNREC monitors the state's conditions against these standards to show trends over time and also provides useful information to the public through real-time, state-wide air quality monitoring. This data can be used to gauge how clean or polluted the air is and what associated health effects might be of concern to citizens on any given day.
In 2017, the most current annual report, Delaware air quality met all NAAQ Standards, except for ground level ozone. Over the last few decades, trends in ambient concentrations of the criteria pollutants have been either level or declining and the number of days with good air quality continues to increase.
If you're interested in learning about indoor air quality, information can be found from Division of Public Health's Healthy Homes program.
Ozone Exceedance Trends

Ground level ozone is a colorless gas that is the main ingredient of smog and is a severe public health concern. Although Delaware and neighboring areas still struggle to be in compliance with national standards for ozone levels, the number of days with unhealthy levels has been declining for more than a decade.

The graph below shows the number of days that have exceeded the NAAQ Standards for ozone. The standards have been strengthened through the years to reflect the best available scientific data of the time. In 1996, the 8-hour standard for ozone was 0.08 parts per million (ppm). The standard was strengthened in 2008 to 0.075 ppm and again during 2015 to 0.070 ppm. The blue bars show the number of exceedance days with the 0.08 ppm standard, the green bars with the 0.075 ppm standard, and the purple bars with the even more stringent 0.070 ppm standard. Look to DNREC's Annual Air Quality Reports for more information.
Annual Ozone Exceedance Days
The graph below depicts the design value for ozone for each county, which is the 3-year average of the 4th highest daily 8-hour average. This is the metric used at the national level to determine whether or not air quality standards for ozone have been met. From this visualization, it is clear that all counties in Delaware have experienced a decrease in ozone concentrations over time.
Ozone 3-Year Average by County
Are we speaking another language? Try the air quality glossary.

Page reviewed 5/14/19